PLAN OF THE WORK XV 
stand the use of the keys. At first sight they will, no doubt, appear 
confusing, but in reality they are exceedingly simple. The system 
upon which they are arranged may be mastered in a few minutes, and 
you will then be surprised at the ease and rapidity with which, even 
in large families, you can “run a bird down.” 
The Key to Families—The scheme of this key which, since its 
appearance in the first edition of the ‘‘Handbook,” has been so widely 
adopted, originated with Ernest Thompson Seton. The key here 
presented is, with some modifications and expansions, based on one 
contributed by Mr. Seton at a time when he was expected to be a joint 
author of this work. Strictly speaking this is not one key but a series 
of keys, one under each order. The orders are placed in a natural 
sequence,—that is, we begin with the oldest, or lowest, forms of birds, 
Loons, Grebes, etc., and end with the most highly developed ones, 
Thrushes, Bluebirds, etc. Two main divisions are given: first, Water 
Birds; second, Land Birds. In no case will it be difficult to decide in 
which of these groups a bird belongs. Now glance over the illustra- 
tions, and select the one which you think most nearly resembles the 
bird you are identifying. At each step, test your decision by reading 
the brief diagnoses of orders and families. In this way you may readily 
place your bird in its proper family. 
The Keys to Species.—If a bird always wore the same plumage, it 
would be a comparatively easy matter to place it in a certain section 
of a key and keep it there. But, unfortunately, not only are the males 
and females of the same species frequently quite unlike, and the young 
different from either, but their plumages may vary with the season. 
Furthermore, an individual of a given species may not only wear two 
very different costumes, but, in doffing one for another, he does it 
gradually, and, in the meantime, appears in changing or transition 
plumage. 
For this reason it has been customary to base keys on only adult 
males. Such keys do very well in the nesting season, when birds are 
in song, and when males constitute probably nine-tenths of the birds 
one sees. But at other times of the year young birds outnumber the 
old ones, and the adults themselves may lose their breeding plumage 
and wear quite a different one. I have, therefore, attempted to make 
keys which will identify a bird in any plumage. To do this, it was 
necessary to use many more specimens than there were species. For 
example, the key to our some 40 species of Warblers is based on 110 
specimens, representing as many phases of plumage. 
With identification as the sole end in view, I have, in the keys, 
abandoned all attempts to follow the current system of classification, 
and, taking color as the most tangible character, have to a great extent 
arranged the species on this character alone. The result, from the sys- 
tematist’s standpoint, is most unnatural. Species of different genera 
are brought into the same subsections, and the more variable species 
may be placed in several widely separated sections. 
